The present invention relates to a universal electric motor with variable air gap.
Stepped electrical motors with variable reluctance are already known, having a rotor formed by a core with cylindrical shape, whose teeth are positioned along the lateral surface, and a coaxial stator having a plurality of excitation windings in a number different from that of the teeth, as shown by FR. No. 2 275 925, for instance.
Such motors are generally complex from the constructive standpoint. Moreover, since the windings are energized according to many periodically alternating phases, such motors give problems in terms of electromagnetic leakage and of the resulting pollution.
The aim of the present invention therefore is to eliminate the aforementioned drawbacks, providing a constructively simple electric motor, which presents reduced leakage and lesser electromagnetic pollution with respect to traditional motors of the same kind.
A further aim of the present invention is to provide an electric motor which can function as well with direct current and with alternating current power supply, that is to say a so-called universal electric motor.
Yet another aim of the present invention is to provide an electric motor which can be started safely in both directions of rotation.
The invention solves the problem of providing a universal electric motor with variable air gap, of the circumferentially equidistant teeth mutually separated by grooves, and a stator provided with an excitation system, which from a general standpoint is characterized in that said excitation system comprises, mounted consecutively distanced on a stator support facing said rotor, at least an electromagnet, provided with an armature and with a winding, a control circuit, provided with a position detector for supplying power to the electromagnet, and a permanent magnet; said electromagnet and said permanent magnet being fastened on said stator support to excite the rotor alternatively, and in adjustable positions to change the direction of rotation of the rotor itself.
Thus, in the motor according to the invention, having a rotor, for instance made of ferromagnetic material with one or more teeth, and a stator with an electromagnet, indifferently powered with direct or alternating current, and with a permanent magnet, positioned in such a way as to provide the direction of rotation and overcome the neutral point, alternating attractions of the electromagnet and of the permanent magnet are created on the teeth of the rotor by means of the control circuit that drives the power supply to the motor.
Although in the present description the invention is described with reference to a rotating motor, it can also be applied to linear motors or to annular linear motors and devices for partial servo-controls.
Moreover, the stator, as described herein, can be movable, and hence the rotor can be fixed, inverting the configuration described above without any other modification.
Among the other advantages noted are excellent efficiency levels thanks to the perfect closure of the magnetic flow between stator and rotor. The total power expended for the rotation of the motor is reduced since the power provided by the electromagnet to repel the permanent magnet from one rotor tooth is substantially identical to that provided by the attraction of the magnet to the rotor tooth of the following step.
The motor according to the invention has particularly simple components, and therefore its cost is reduced.
The power of the motor can be varied by increasing the number of electromagnets and permanent magnets on the stator from a single pair to multiple pairs thereof, or the number of single electromagnets or permanent magnets.
The motor according to the invention can be applied, instead of to a rotor made of ferromagnetic material, to a rotor whose teeth are polar expansions permanently magnetized with the same polarity as the permanent magnet of the excitation system, or opposite thereto. In this case, the motor functions by repulsion or, respectively, by attraction and for the offset required for its motion it is the electromagnet winding that is off-center with respect to the polar pitch, to the right or to the left of the desired direction of rotation. Therefore, the power of the electromagnet serves to win the repulsion or attraction force of the permanent magnet and to provide the desired power to the motor shaft.
Further features and advantages of the invention shall be made more readily apparent from the content of the detailed description that follows, of embodiments illustrated purely by way of non limiting indication in the accompanying drawings.